We all have a personal bubble, an invisible zone of privacy around our bodies. When strangers cross this boundary, it makes us feel uncomfortable. But not all of us – Daniel Kennedy from the California Institute of Technology has been studying a woman known only as SM, who lacks any sense of personal space.

SM suffers from a rare genetic disorder called Urbach-Wiethe disease, that causes parts of the brain’s temporal lobes to harden and waste away. This brain damage has completely destroyed SM’s amygdalae, a pair of small, almond-shaped structures that help us to process emotions.

Kennedy asked her to say when she felt most comfortable as a female experimenter walked towards her. On average, she preferred a distance of